In order to satisfy performance required of vehicle mounted radars with low cost, various radar modulation schemes have been used. As examples of such radar modulation schemes, a frequency-modulated continuous wave (FMCW) technique, a two-frequency CW technique, and so on are disclosed in Reference 2, RCR TR-26, “Automotive Radar Research and Development Report” edited by Research & Development Center for Radio System, July 1993. The above FMCW and two-frequency CW are radar schemes for detecting the speeds and the distances and the distances of moving objects.
U.S. Pat. No. 5,963,163 discloses an advanced scheme of two-frequency CW.